Add preopt scripts to mainline.

These scripts support art preopting in system_other, which is
a generically useful thing to keep on mainline.

Note that the preloads_copy script should also be added, but
that needs some work to be done (b/116714695).

Bug: 80410283
Test: lunch mainline_arm64; m nothing
Change-Id: I693e17ac0f61f2417ced639d1fdfe164c54341a9